page_title: Mercury-Redstone 4
section_title: Launch
hierarchical_section_title: Mercury-Redstone 4 / Mission description / Launch
caption_attribution_description: English: Liftoff of Mercury-Redstone 4 (MR-4), Liberty Bell 7, on July 21, 1961. The MR-4 mission was the second U.S. manned sub-orbital flight and carried astronaut Virgil "Gus" Grissom into space aboard the Liberty Bell 7 spacecraft for a duration of 15-1/2 minutes.
context_page_description: Mercury-Redstone 4 was the second United States human spaceflight, on July 21, 1961. The suborbital Project Mercury flight was launched with a Mercury-Redstone Launch Vehicle, MRLV-8. The spacecraft, Mercury capsule #11, was nicknamed the Liberty Bell 7. It was piloted by astronaut Virgil "Gus" Grissom.
  The spaceflight lasted 15 minutes 30 seconds, reached an altitude of more than 102.8 nautical miles, and flew 262.5 nautical miles downrange, landing in the Atlantic Ocean. The flight went as expected until just after splashdown, when the hatch cover, designed to release explosively in the event of an emergency, accidentally blew. Grissom was at risk of drowning, but was recovered safely via a U.S. Navy helicopter. The spacecraft sank into the Atlantic and was not recovered until 1999.
context_section_description: Grissom later admitted at the postflight debriefing that he was "a bit scared" at liftoff, but he added that he soon gained confidence along with the acceleration increase. Hearing the engine roar at the pedestal, he thought that his elapsed-time clock had started late. Like Shepard, he was amazed at the smooth quality of the liftoff, but then he noticed gradually more severe vibrations. These were never violent enough to impair his vision.
  Grissom's cabin pressure sealed off at the proper altitude, about 27,000 ft (8.2 km), and he felt elated that the environmental control system was in good working order. The cabin and suit temperatures, respectively about 57.5 and 97 °F (14.2 and 36.1 °C) were quite comfortable. Watching his instruments for the pitch rate of the Redstone, Grissom saw it follow directions as programmed, tilting over at about one deg/s.
  During a 3 g (29 m/s²) acceleration on the up-leg of his flight, Grissom noticed a sudden change in the color of the horizon from light blue to jet black. His attention was distracted by the noise of the tower-jettison rocket firing on schedule. Grissom felt the separation, and he watched the tower through the window as it drifted off, trailing smoke, to his right. At two minutes and 22 seconds after launch, the Redstone's Rocketdyne engine cut off after building a speed of 6,561 ft/s (2,000 m/s). Grissom had a strong sensation of tumbling during the transition from high to zero acceleration, and, while he had become familiar with this sensation in centrifuge training, for a moment he lost his bearings.
  The Redstone coasted for 10 seconds after its engine cut off; then a sharp report signaled that the posigrade rockets were popping the spacecraft loose from the booster. Although Grissom peered out his window throughout his ship's turnaround maneuver, he never caught sight of his booster.
caption: Launch of Mercury-Redstone 4 at Cape Canaveral Air Force Station Launch Complex 5
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